Multi-layer circuit board

ABSTRACT

A multi-layer circuit board includes first, second, third, fourth, fifth, sixth and seventh insulating substrates disposed sequentially one above the other; first, second, third and fourth signal wiring layers; first, second and third ground wiring layers; and a power wiring layer. Each of the first and seventh insulating substrates has a thickness ranging from 2.5 to 7.5 mil. Each of the second and sixth insulating substrates has a thickness ranging from 3 to 13 mil. Each of the third and fifth insulating substrates has a thickness ranging from 3 to 15 mil. The fourth insulating substrate has a thickness ranging from 2 to 6 mil. The first signal wiring layer has a first resistance with respect to the first ground wiring layer. The second signal wiring layer has a second resistance with respect to the first and second ground wiring layers. The third signal wiring layer has a third resistance with respect to the third ground wiring layer and the power wiring layer. The fourth signal wiring layer has a fourth resistance with respect to the third ground wiring layer. The first, second, third and fourth resistances are within the range of 49.5 to 60.5 ohms.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a multi-layer circuit board, more particularlyto a multi-layer circuit board which can achieve impedance matching toresult in reduced high speed signal reflection and reducedelectromagnetic interference.

2. Description of the Related Art

A conventional multi-layer circuit board with eight wiring layersgenerally has a thickness of 1.6 mm or 1.2 mm. Reference is made to FIG.1, which shows a multi-layer circuit board with a thickness of 1.2 mm.As shown, the circuit board includes: first, second, third, fourth,fifth, sixth and seventh insulating substrates (F1), (F2), (F3), (F4),(F5), (F6), (F7) disposed sequentially one above the other; a firstsignal wiring layer (S1) disposed on one side of the first insulatingsubstrate (F1) opposite to the second insulating substrate (F2); a firstground wiring layer (GND1) disposed between the first and secondinsulating substrates (F1), (F2); a second signal wiring layer (S2)disposed between the second and third insulating substrates (F2), (F3);a second ground wiring layer (GND2) disposed between the third andfourth insulating substrates (F3), (F4); a power wiring layer (POWER)disposed between the fourth and fifth insulating substrates (F4), (F5);a third signal wiring layer (S3) disposed between the fifth and sixthinsulating substrates (F5), (F6); a third ground wiring layer (GND3)disposed between the sixth and seventh insulating substrates (F6), (F7);and a fourth signal wiring layer (S4) disposed on one side of theseventh insulating substrate (F7) opposite to the sixth insulatingsubstrate (F6). The first, second, third, fourth, fifth, sixth andseventh insulating substrates (F1), (F2), (F3), (F4), (F5), (F6), (F7),the first, second, third and fourth signal wiring layers (S1), (S2),(S3), (S4), the first, second and third ground wiring layers (GND1),(GND2), (GND3), and the power wiring layer (POWER) are press-bonded toeach other to form the circuit board with a thickness of about 1.2 mm.The first and fourth signal wiring layers (S1), (S4) are adapted to bemounted with electronic components (not shown) thereon.

Each of the first and seventh insulating substrates (F1), (F7) has athickness (H4) of about 2.5 mil. Each of the second, fourth and sixthinsulating substrates (F2), (F4), (F6) has a thickness (H3), (H1) ofabout 8 mil. Each of the third and fifth insulating substrates (F3),(F5) has a thickness (H2) of about 5 mil. Each of the first, third,fifth and seventh insulating substrates (F1), (F3), (F5), (F7) is madefrom a polyester prepreg. Each of the second, fourth and sixthinsulating substrates (F2), (F4), (F6) is made from a fibrous corematerial that contains paper or glass fibers. In this structure, thefirst signal wiring layer (S1) has a first resistance (Rs1) with respectto the first ground wiring layer (GND1). The second signal wiring layer(S2) has a second resistance (Rs2) with respect to the first and secondground wiring layers (GND1), (GND2). The third signal wiring layer (S3)has a third resistance (Rs3) with respect to the third ground wiringlayer (GND3) and the power wiring layer (POWER). The fourth signalwiring layer (S4) has a fourth resistance (Rs4) with respect to thethird ground wiring layer (GND3). The first and fourth resistances(Rs1), (Rs4) are about 44 ohms. The second and third resistances (Rs2),(Rs3) are about 55 ohms.

FIG. 2 shows a multi-layer circuit board with a thickness of 1.6 mm. The1.6 mm circuit board differs from the aforementioned 1.2 mm circuitboard in that the thickness (H4) of the first and seventh insulatingsubstrates (F1), (F7) is about 9.5 mil. As a result, the first andfourth resistances (Rs1), (Rs4) are about 76.4 ohms, and the second andthird resistances (Rs2), (Rs3) are about 51 ohms. Due to theirconstruction, the conventional circuit boards shown in FIGS. 1 and 2suffer from the following drawbacks:

1. Serious High Speed Signal Reflection

According to the standard theoretical values determined by Intel, theresistance between two adjacent wiring layers for a circuit board duringhigh speed signal transmission is preferably within the range of 55±10%Ω, i.e., between 49.5 Ω and 60.5 Ω. However, the value of the first andfourth resistances (Rs1), (Rs4) of the aforementioned conventional 1.2mm circuit board falls outside the preferred range recommended by Intel,and there is additionally a difference of about 11 ohms between thevalue of the first and fourth resistances (Rs1), (Rs4) and that of thesecond and third resistances (Rs2), (Rs3). Such a difference will resultin an impedance mismatch. Thus, when a high speed signal is beingtransmitted through the conventional 1.2 mm circuit board and passesfrom the first or fourth wiring layer (S1) or (S4) to the second orthird wiring layer (S2) or (S3) reflection of the signal will result,thereby adversely affecting signal transmission. Likewise, the value ofthe first and fourth resistances (Rs1), (Rs4) of the aforementionedconventional 1.6 mm circuit board falls outside the theoretical range,and there is a large difference of 25.4 ohms between the value of thefirst and fourth resistances (Rs1), (Rs4) and that of the second andthird resistances (Rs2), (Rs3). The signal reflection problem istherefore very serious. The reflection index of high-speed signals forthe 1.2 mm circuit board can be calculated as follows:$\rho = {\frac{{Zl} - {Zo}}{{Zl} + {Zo}} = {\frac{{Rs1} - {Rs2}}{{Rs1} + {Rs2}} = 0.111}}$

The reflection index for the 1.6 mm circuit board can be calculated in asimilar manner to result in 0.199.

(2)Weakened magnetic flux counteraction: As reflection of high speedsignals will generate standing waves, which will increaseelectromagnetic radiation of the high speed signals, the magnetic fluxcounteraction of the circuit board is weakened, thereby resulting inexcessively high electromagnetic interference.

SUMMARY OF THE INVENTION

Therefore, the main object of the present invention is to provide amulti-layer circuit board which can achieve impedance matching to resultin reduced high speed signal reflection and reduced electromagneticinterference.

Accordingly, a multi-layer circuit board of the present inventionincludes: first, second, third, fourth, fifth, sixth and seventhinsulating substrates disposed sequentially one above the other; a firstsignal wiring layer disposed on one side of the first insulatingsubstrate opposite to the second insulating substrate; a first groundwiring layer disposed between the first and second insulatingsubstrates; a second signal wiring layer disposed between the second andthird insulating substrates; a second ground wiring layer disposedbetween the third and fourth insulating substrates; a power wiring layerdisposed between the fourth and fifth insulating substrates; a thirdsignal wiring layer disposed between the fifth and sixth insulatingsubstrates; a third ground wiring layer disposed between the sixth andseventh insulating substrates; and a fourth signal wiring layer disposedon one side of the seventh insulating substrate opposite to the sixthinsulating substrate. Each of the first and seventh insulatingsubstrates has a thickness ranging from 2.5 to 7.5 mil. Each of thesecond and sixth insulating substrates has a thickness ranging from 3 to13 mil. Each of the third and fifth insulating substrates has athickness ranging from 3 to 15 mil. The fourth insulating substrate hasa thickness ranging from 2 to 6 mil. The first signal wiring layer has afirst resistance with respect to the first ground wiring layer. Thesecond signal wiring layer has a second resistance with respect to thefirst and second ground wiring layers. The third signal wiring layer hasa third resistance with respect to the third ground wiring layer and thepower wiring layer. The fourth signal wiring layer has a fourthresistance with respect to the third ground wiring layer. The first,second, third and fourth resistances are within the range of 49.5 to60.5 ohms.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will becomeapparent in the following detailed description of the preferredembodiments with reference to the accompanying drawings, of which:

FIG. 1 is a schematic view of a conventional multi-layer circuit boardwith a thickness of about 1.2 mm;

FIG. 2 is a schematic view of another conventional multi-layer circuitboard with a thickness of about 1.6 mm;

FIG. 3 is a schematic view of the first preferred embodiment of amulti-layer circuit board with a thickness of about 1.2 mm according tothe present invention;

FIG. 4 is sectional view of the first preferred embodiment in part;

FIG. 5 is another sectional view of the first preferred embodiment inpart; and

FIG. 6 is a schematic view of the second preferred embodiment of amulti-layer circuit board with a thickness of about 1.6 mm according tothe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before the present invention is described in greater detail, it shouldbe noted that like elements are denoted by the same reference numeralsthroughout the disclosure.

Referring to FIGS. 3 to 5, the first preferred embodiment of amulti-layer circuit board 6 according to the present invention is shownto include first, second, third, fourth, fifth, sixth and seventhinsulating substrates (L1), (L2), (L3), (L4), (L5), (L6), (L7) disposedsequentially one above the other; a first signal wiring layer (S1)disposed on one side of the first insulating substrate (L1) opposite tothe second insulating substrate (L2); a first ground wiring layer (GND1)disposed between the first and second insulating substrates (L1), (L2);a second signal wiring layer (S2) disposed between the second and thirdinsulating substrates (L2), (L3); a second ground wiring layer (GND2)disposed between the third and fourth insulating substrates (L3), (L4);a power wiring layer (POWER) disposed between the fourth and fifthinsulating substrates (L4), (L5); a third signal wiring layer (S3)disposed between the fifth and sixth insulating substrates (L5), (L6); athird ground wiring layer (GND3) disposed between the sixth and seventhinsulating substrates (L6), (L7); and a fourth signal wiring layer (S4)disposed on one side of the seventh insulating substrate (L7) oppositeto the sixth insulating substrate (L6). The first, second, third andfourth signal wiring layers (S1), (S2), (S3), (S4) are generally madefrom copper foil, and the first and fourth signal wiring layers (S1),(S4) are adapted to be mounted with electronic components (not shown)thereon.

The first, second, third, fourth, fifth, sixth and seventh insulatingsubstrates (L1), (L2), (L3), (L4) (L5), (L6), (L7), the first, second,third and fourth signal wiring layers (S1), (S2), (S3), (S4), the first,second and third ground wiring layers (GND1), (GND2), (GND3), and thepower wiring layer (POWER) are press-bonded to each other to form thecircuit board 6 with a thickness of about 1.2 mm.

During press-bonding of the circuit board 6, the second ground wiringlayer (GND2) and the power wiring layer (POWER) are disposed to sandwichthe fourth insulating substrate (L4). Then, the second signal wiringlayer (S2) and the second ground wiring layer (GND2), and the thirdsignal wiring layer (S3) and the power wiring layer (POWER) are disposedto sandwich the third and fifth insulating substrates (L3), (L5),respectively. The first ground wiring layer (GND1) and the second signalwiring layer (S2), and the third ground wiring layer (GND3) and thethird signal wiring layer (S3) are disposed to sandwich the second andsixth insulating substrates (L2), (L6). Finally, the first signal wiringlayer (S1) and the first ground wiring layer (GND1), and the fourthsignal wiring layer (S4) and the third ground wiring layer (GND3) aredisposed to sandwich the first and seventh insulating substrates (L1),(L7) to constitute the 1.2 mm multi-layer circuit board 6.

According to the present invention, each of the first and seventhinsulating substrates (L1), (L7) has a thickness (H4) ranging from 2.5to 7.5 mil. Each of the second and sixth insulating substrates (L2),(L6) has a thickness (H3) ranging from 3 to 13 mil. Each of the thirdand fifth insulating substrates (L3), (L5) has a thickness (H2) rangingfrom 3 to 15 mil. The fourth insulating substrate (L4) has a thickness(H1) ranging from 2 to 6 mil. The first signal wiring layer (S1) has afirst resistance (Rs1) with respect to the first ground wiring layer(GND1). The second signal wiring layer (S2) has a second resistance(Rs2) with respect to the first and second ground wiring layers (GND1),(GND2). The third signal wiring layer (S3) has a third resistance (Rs3)with respect to the third ground wiring layer (GND3) and the powerwiring layer (POWER). The fourth signal wiring layer (S4) has a fourthresistance (Rs4) with respect to the third ground wiring layer (GND3).With the thicknesses of the insulating substrates (L1), (L2), (L3),(L4), (L5) (L6), (L7) controlled to be within the aforementioned ranges,the first, second, third and fourth resistances (Rs1), (Rs2), (Rs3),(Rs4) can be kept within the range of 49.5 to 60.5 ohms recommended byIntel for high speed signal transmission so as to achieve impedancematching.

At least one of the first, third, fifth and seventh insulatingsubstrates (L1), (L3), (L5), (L7) is made from a polyester prepreg. Atleast one of the second, fourth and sixth insulating substrates (L2),(L4), (L6) is made from a fibrous core material that contains paperfibers or glass fibers.

According to the first preferred embodiment, each of the first andfourth signal wiring layers (S1), (S4) has a thickness of about 1.4 mil.Each of the second and third signal wiring layers (S2), (S3), the first,second and third ground wiring layers (GND1), (GND2), (GND3), and thepower wiring layer (POWER) has a thickness of about 0.7 mil. Each of thefirst and seventh insulating substrates (L1), (L7) has a preferredthickness (H4) of 4.5±2 mil, more preferably 4.5 mil. Each of the secondand sixth insulating substrates (L2), (L6) has a preferred thickness(H3) of 6±3 mil, more preferably 6 mil. Each of the third and fifthinsulating substrates (L3), (L5) has a preferred thickness (H2) of 7±4mil, more preferably 7 mil. The fourth insulating substrate (L4) has apreferred thickness (H1) of 4 mil. Preferably, the thicknesses (H4) ofthe first and seventh insulating substrates (L1), (L7) are equal. Thethicknesses (H3) of the second and sixth insulating substrates (L2),(L6) are equal. The thicknesses (H2) of the third and fifth insulatingsubstrates (L3), (L5) are equal.

The calculation of the approximate thickness of each of the insulatingsubstrates (L1), (L2), (L3), (L4) (L5), (L6) and (L7) is explained inthe following description.

Firstly, the value of the first resistance and fourth resistance (Rs1),(Rs4) is calculated using the following Formula (1): $\begin{matrix}{{Rs1} = {{Rs4} = {\frac{87}{\sqrt{E_{R} + 1.41}}\ln \left\{ \frac{5.98{H4}}{{0.8W} + {T1}} \right\}}}} & 1\end{matrix}$

wherein E_(R) is the dielectric coefficient and is equal to 4.5; H4 isthe thickness of the first and seventh insulating substrates (L1), (L7);W is the width of traces of the first and fourth signal wiring layers(S1), (S4) and is within the range of 2 to 8 mil and is equal to 5 milin this preferred embodiment; and T1 is the thickness of the first andfourth signal wiring layers (S1), (S4) and is equal to 1.4 mil.

Next, the value of the second and third resistances (Rs2), (Rs3) isobtained using the following Formula (2): $\begin{matrix}{{Rs2} = {{Rs3} = {\frac{60}{\sqrt{E_{R}}}\ln \left\{ \frac{4\left( {{H3} + {H2}} \right)}{0.67\pi \quad {W\left( {0.8 + \frac{T2}{W}} \right)}} \right\}}}} & 2\end{matrix}$

wherein E_(R) is the dielectric coefficient and is equal to 4.5; H2 isthe thickness of the third and fifth insulating substrates (L3), (L5);H3 is the thickness of the second and sixth insulating substrates (L2),(L6); T2 is the thickness of the second and third signal wiring layers(S2), (S3) and is equal to 0.7 mil; and W is the width of traces of thesecond and third signal wiring layers (S2), (S3) and is within the rangeof 2 to 8 mil. In this preferred embodiment, W is equal to 5 mil.

2H 4+2H 3+2H 2+1H 1+2T 1+6T2 ≅1.2 mm . . . 3

In addition, the total thickness of the circuit board should be equal to1.2 mm (equivalent to about 47 mil) or within a tolerance range thereof,as expressed by the Formula (3). Based on the above Formula (3), thepreferred value of thickness of each of the insulating substrates can beobtained. That is, when H1, the thickness of the fourth insulatingsubstrate (L4) is within the range of 2 to 6 mil, it is preferably equalto 4 mil. When H2, the thickness of each of the third and fifthinsulating substrates (L3), (L5) is within the range of 3 to 11 mil, itis preferably equal to 7 mil. When H3, the thickness of the second andsixth insulating substrates (L2), (L6) is within the range of 3 to 9mil, it is preferably equal to 6 mil. When H4, the thickness of each ofthe first and seventh insulating substrates (L1), (L7) is within therange of 2.5 to 6.5 mil, it is preferably equal to 4.5 mil. As such, thefirst resistance (Rs1) of the first signal wiring layer (S1) withrespect to the first ground wiring layer (GND1) is equal to the fourthresistance (Rs4) of the fourth signal wiring layer (S4) with respect tothe third ground wiring layer (GND3) and is equal to 58 ohms, i.e.,Rs1=Rs4=58 Ω. The second resistance (Rs2) of the second signal wiringlayer (S2) with respect to the first and second ground wiring layers(GND1), (GND2) is equal to the third resistance (Rs3) of the thirdsignal wiring layer (S3) with respect to the power wiring layer (POWER)and the third ground wiring layer (GND3) and is equal to 52 ohms, i.e.,Rs2=Rs3=52 Ω. It is noted that these resistance values fall within thetheoretical range of 55 Ω±10%, and have a difference of only 6 ohms. Assuch, the reflection index ρ is reduced to 0.05, which is lower than thereflection index (ρ=0.11) in the prior art. Besides, the total thicknessof the circuit board 6 fulfills Formula 3 (2H4+2H3+2H2+1H1+2T1+6T2), andis equal to 2×4.5 mil+2×6 mil+2×7 mil+1×4 mil+2×1.4 mil+6×0.7 mil=46mil≈1.2 mm (within tolerance range).

FIG. 6 shows the second preferred embodiment of a multi-layer circuitboard 6′ according to the present invention. The difference between thisembodiment and the previous embodiment is that the circuit board 6′ hasa thickness of about 1.6 mm, that each of the first and seventhsubstrates (L1′), (L7′) has a preferred thickness of 5.5±2 mil, morepreferably 5.5 mil, that each of the second and sixth insulatingsubstrates (L2′), (L6′) has a preferred thickness of 10±3 mil, morepreferably 10 mil, and that each of the third and fifth insulatingsubstrates (L3′), (L5′) has a preferred thickness of 11±4 mil, morepreferably 11 mil. The first signal wiring layer (S1) has a firstresistance (Rs1′) with respect to the first ground wiring layer (GND1).The second signal wiring layer (S2) has a second resistance (Rs2′) withrespect to the first and second ground wiring layers (GND1), (GND2) Thethird signal wiring layer (S3) has a third resistance (Rs3′) withrespect to the third ground wiring layer (GND3) and the power wiringlayer (POWER) The fourth signal wiring layer (S4) has a fourthresistance (Rs4′) with respect to the third ground wiring layer (GND3).

Under the condition that the sum according to Formula (3) issubstantially equal to 1.6 mm (approximately 64 mil) and that theresistance values fall within the theoretical range recommended byIntel, the value of (Rs1′), (Rs4′) and the value of (Rs2′), (Rs3′) arefirst calculated using Formulae (1) and (2) so as to obtain thepreferred thickness of each of the insulating substrates. Of theseparameters, the width of traces of the signal wiring layers is withinthe range of 2 to 8 mil, and is preferably 6 mil, as is mostly adoptedfor 1.6 mm circuit boards. It is found that when H1 is within the rangeof 2 to 6 mil, H1 is preferably 4 mil. When H2 is within the range of 7to 15 mil, H2 is preferably 11 mil. When H3 is within the range of 7 to13 mil, H3 is preferably 10 mil. When H4 is within the range of 3.5 to7.5 mil, H4 is preferably 5.5 mil. As such, the first resistance (Rs1′)is equal to the fourth resistance (Rs4′) and is equal to 60 ohms, i.e.,(Rs1′)=(Rs4′)=60 Ω. The second resistance (Rs2′) is equal to the thirdresistance (Rs3′) and is equal to 60 ohms, i.e., (Rs2′)=(Rs3′)=60 Ω.Both of these resistance values fall within the range of 49.5 to 60.5ohms recommended by Intel. Besides, the reflection index is reduced tozero. Moreover, the thickness of the circuit board 6′ according toFormula (3) is substantially equal to 1.6 mm:2H4+2H3+2H2+1H1+2T1+6T2=2×5.5 mil+2×10 mil+1×4 mil+2×1.4 mil+6×0.7mil=64 mil≈1.6 mm (within tolerance range).

Accordingly, the multi-layer circuit board of the present invention hasthe following advantages:

1. Reduced High Speed Signal Reflection

Since the resistances in both of the first and second preferredembodiments fall within the recommended range of 55±10%, and since thereflection indexes are substantially low as compared to those in theprior art, reflection of high speed signals can: be significantlyreduced or eliminated to make the circuit board very suitable for highspeed signal transmission.

2. Reduced Electromagnetic Interference

As a result of reduced high speed signal reflection, generation ofstanding waves is not likely. Hence, magnetic flux counteraction can beenhanced to reduce electromagnetic interference to meet current EMIstandards.

3. Better Adaptability for High Speed Signal Layout

In view of the aforementioned advantages, the circuit board of thisinvention is suited for high speed signal layout to meet the currenttrend in the industry toward high speed signal development and toenhance market value of products and market competitiveness.

4. Enhanced Layout Time Efficiency

Due to impedance matching, there is no need to alter the width of tracesof the signal wiring layers, thereby improving the layout timeefficiency.

While the present invention has been described in connection with whatis considered the most practical and preferred embodiments, it isunderstood that this invention is not limited to the disclosedembodiments but is intended to cover various arrangements includedwithin the spirit and scope of the broadest interpretation so as toencompass all such modifications and equivalent arrangements.

I claim:
 1. A multi-layer circuit board comprising: first, second,third, fourth, fifth, sixth and seventh insulating substrates disposedsequentially one above the other; a first signal wiring layer disposedon one side of said first insulating substrate opposite to said secondinsulating substrate; a first ground wiring layer disposed between saidfirst and second insulating substrates; a second signal wiring layerdisposed between said second and third insulating substrates; a secondground wiring layer disposed between said third and fourth insulatingsubstrates; a power wiring layer disposed between said fourth and fifthinsulating substrates; a third signal wiring layer disposed between saidfifth and sixth insulating substrates; a third ground wiring layerdisposed between said sixth and seventh insulating substrates; and afourth signal wiring layer disposed on one side of said seventhinsulating substrate opposite to said sixth insulating substrate;wherein each of said first and seventh insulating substrates has athickness ranging from 2.5 to 7.5 mil; wherein each of said second andsixth insulating substrates has a thickness ranging from 3 to 13 mil;wherein each of said third and fifth insulating substrates has athickness ranging from 3 to 15 mil; wherein said fourth insulatingsubstrate has a thickness ranging from 2 to 6 mil; wherein said firstsignal wiring layer has a first resistance with respect to said firstground wiring layer, said second signal wiring layer having a secondresistance with respect to said first and second ground wiring layers,said third signal wiring layer having a third resistance with respect tosaid third ground wiring layer and said power wiring layer, said fourthsignal wiring layer having a fourth resistance with respect to saidthird ground wiring layer; and wherein said first, second, third andfourth resistances are within the range of 49.5 to 60.5 ohms.
 2. Themulti-layer circuit board of claim 1, wherein at least one of saidfirst, third, fifth and seventh insulating substrates is made from apolyester prepreg.
 3. The multi-layer circuit board of claim 1, whereinat least one of said second, fourth and sixth insulating substrates ismade from a fibrous core material.
 4. The multi-layer circuit board ofclaim 3, wherein the core material contains paper fibers.
 5. Themulti-layer circuit board of claim 3, wherein the core material containsglass fibers.
 6. The multi-layer circuit board of claim 1, wherein thethicknesses of said first and seventh insulating substrates are equal.7. The multi-layer circuit board of claim 1, wherein the thicknesses ofsaid second and sixth insulating substrates are equal.
 8. Themulti-layer circuit board of claim 1, wherein the thicknesses of saidthird and fifth insulating substrates are equal.
 9. The multi-layercircuit board of claim 1, wherein: each of said first and fourth signalwiring layers has a thickness of about 1.4 mil; and each of said secondand third signal wiring layers, said first, second and third groundwiring layers, and said power wiring layer has a thickness of about 0.7mil.
 10. The multi-layer circuit board of claim 1, wherein: each of saidfirst and seventh insulating substrates has a thickness of 4.5±2 mil;each of said second and sixth insulating substrates has a thickness of6±3 mil; each of said third and fifth insulating substrates has athickness of 7±4 mil; and said first, second, third, fourth, fifth,sixth and seventh insulating substrates, said first, second, third andfourth signal wiring layers, said first, second and third ground wiringlayers, and said power wiring layer are press-bonded to each other toform said circuit board with a thickness of about 1.2 mm.
 11. Themulti-layer circuit board of claim 10, wherein: each of said first andseventh insulating substrates has a thickness of 4.5 mil; each of saidsecond and sixth insulating substrates has a thickness of 6 mil;. eachof said third and fifth insulating substrates has a thickness of 7 mil;and said fourth insulating substrate has a thickness of 4 mil.
 12. Themulti-layer circuit board of claim 1, wherein: each of said first andseventh insulating substrates has a thickness of 5.5±2 mil; each of saidsecond and sixth insulating substrates has a thickness of 10±3 mil; eachof said third and fifth insulating substrates has a thickness of 11±4mil; and said first, second, third, fourth, fifth, sixth and seventhinsulating substrates, said first, second, third and fourth signalwiring layers, said first, second and third ground wiring layers, andsaid power wiring layer are press-bonded to each other to form saidcircuit board with a thickness of about 1.6 mm.
 13. The multi-layercircuit board of claim 12, wherein: each of said first and seventhinsulating substrates has a thickness of 5.5 mil; each of said secondand sixth insulating substrates has a thickness of 10 mil; each of saidthird and fifth insulating substrates has a thickness of 11 mil; andsaid fourth insulating substrate has a thickness of 4 mil.